Currently, there is a need to deliver electric power to implanted medical devices such as artificial hearts and ventricle assist devices. It is possible to deliver power non-invasively through electromagnetic energy transmitted through the skin. However, problems can arise related to the implanted secondary, which receives power from the external primary. In one respect, the system can operate over limited power and/or coupling ranges. Here, the resonant network that transfers power from the primary to the secondary is typically designed both for startup conditions that momentarily require a high power and for normal operating conditions that require less power. Operating the system in both of these conditions using the same resonant network can limit the power and coupling ranges that are available to the system. In another respect, the secondary can heat-up and injure the subject due to inadvertent non-optimal coupling, including possibly over-coupling or under-coupling, between the primary and the secondary. Because the secondary is implanted and thus relatively inaccessible, a problem can arise and cause injury before the user or the system is aware of the problem. Prior art systems fail to provide mechanisms for addressing these and other issues that concern transfer of electromagnetic energy to implanted medical devices. These and other deficiencies of the prior art are addressed herein.